The invention relates to pumps, but more particularly, the invention relates to piston rubbers as used in slurry-type pumps.
Piston rubbers form the major portion of a pump piston by defining a major cylindrical portion and piston seal. Piston rubbers are used in reciprocating, usually double acting, slurry-type pumps such as used by the oil industry for pumping mud during drilling operations. Two piston rubbers are used in each cylinder bore with a disc piston that is connected to an axially reciprocating rod. A piston rubber has a generally cylindrically shaped elastomeric body with a lip-seal end and a reinforced end. Piston rubbers are arranged "back-to-back" with their reinforced ends abutting the disc piston so that the lip-seals face axially away from each other and engage the cylinder bore.
Some of the better piston rubbers (e.g., those piston rubbers having longer service lives) have a multi-layered fabric reinforcement fabricated by stacking a plurality of annular rings together which are individually cut in "cookie" fashion from flat, square woven fabric. A "breaker ply" of heavy gauge fabric may be positioned on the top of the reinforcement stack so that it interfaces with the elastomeric body to provide a modulus transition for improved flex fatigue.
While such piston rubbers provide good service in their intended working environment, their manufacture and use are not free of problems. The "cookie cutter" method of forming the individual fabric plies leaves surrounding flat stock and centers as an economic waste. Sometimes, the stacked plies drift from each other during the molding process and identify points where delaminations of the plies may initiate when the piston rubber is in use. The ends of threads forming the fabric are located along the circumference of the piston rubber end and are subject to wear and wicking which may result in ply delaminations. Once wear begins, support of the piston body is reduced which may cause leakage past the piston and corresponding reduced pumping pressures. Should a burr or rock or other foreign debri arise in a cylinder bore in which a piston rubber is operating, it tears at the thread ends of the plies causing premature delamination with associated loss of pumping pressure.